I got the dreaded P0301 misfire code over the weekend. My 2012 Mini Cooper Hardtop non-aspirated base model R56 with only 44K miles on it has been hesitating now and then for sometime, but seemed to run better in Sport mode and a heavy foot. I had been considering replacing the trans fuild, but then I got "The Code." After the half-slash engine check light came on it kind of went into semi-limp mode or just started hesitating even more. Pulled over, turned it off, then restarted it and the light went away. The car ran okay after that for the rest of the day, but still had hesitations now and then.

The next day it happened again when leaving a traffic light as the first car. This time it wouldn’t go and did feel like complete limp mode had engaged. I quickly turn my emergency flashers on to warn others and managed to limp the car through the intersection into a parking lot. Once again I turned it off and back on. The light went out and I was able to drive it home with hesitations.

After that I started researching what this code meant. I found things like: spark plugs, coils, fuel injectors, wiring, fuel pump, oxygen sensor and even catalytic converter listed by others. That scared me a little bit as my brother and his son both went through modern car computer error code issues recently; my brother got bit for about $6,000 and his son about $3,000. That isn’t something I wanted to go through right now that’s for sure.

On 4th of July morning I started the hunt by seeing if I could make it happen again. That turned out to be easily done, so I parked it and started inspecting the engine, wiring, and trying to find anything that looked unusual. Couldn’t find a thing on the surface inspection, so I popped the coil wires off and pulled the coils keeping track of which one came from what cylinder. Next I pulled the spark plugs. They all looked a nice coco brown and the #1 plug wasn’t any different than the others, but the spark plug gaps looked huge from what I am used to seeing. In addition, the ends of the electrodes looked like they were worn to a knifes edge instead of being rectangular with squared-off edges.

A little more research indicated that the gap should be 1.00mm (0.0394”); mine were all at ~0.050”. So I re-gapped them all to 0.040” and re-installed them. When I put the coils back on I swapped the #1 & #2 coils and left #3 & #4 on the same cylinder they came off of. My thought was if the error code moves from #1 to #2, then the #1 coil is the problem.

To my surprise, the car ran like a bat out of hell after just re-gapping the spark plugs and I haven’t gotten any hesitation or error codes since. I’m a happy camper!

It seems the out of spec worn spark plug gaps were the problem at only 44K miles. I have plug replacement on my maintenance schedule at 60K, but now I’m changing that to 40K and have ordered a new set of DENSO 3444 plugs ($36 for the set of 4 on eBay delivered) to replace the worn out OEM ones. Remember this is a Justa, not an S Turbo model.

I’m posting this because I can see this simple issue easily turning into a +/-$1,000 visit at the dealer; replacing part after part until they finally stumble upon replacing the spark plugs 16K miles BEFORE they are supposed to be due at some crazy outrageous stealer price.

Hope this gives other Justa owners with a half-slash yellow engine check light and P0301 (2, 3 or 4) Misfire Code a place to start without bending over...

Cheers!

 

Good write up, thx for posting..

 

The moral of this story is always keep you engine compartment clean so it’s easy to check for loose or worn wires/connections, then check normal wear parts that might be related to the error code first. In a misfire case like this you can also run a bottle of quality “complete” fuel system cleaner through a tank of gas too. Hopefully your car will still be operable to do that. If you are not sure the air cleaner is clean, then check that as well.

I generally run a can of BG-44K in a tank of gas at about 60,000 miles in all my cars, then one more normal tank of gas and do an oil/filter change right after. BG-44K is good stuff, but very toxic and it can get by the rings a little bit and possibly contaminate the oil, so it’s best to complete an oil/filter change shortly after any heavy duty treatment like that. This might do wonders for the carbon buildup issues the S Turbo models seem to have.

I’ll be running a can through my Mini NOW (early), before the new plugs go in and next oil/filter change just to be safe.

 

Following up on this post...

The light has stayed off. I ran a full tank of gas with a can of BG-44K in it and another full tank of straight gas through the engine. Now I'm ready to change the oil, filter and spark plugs, but noticed the DENSO plugs have larger gaps than the BMW MINI specifications.

Question for those of you running DENSO spark plugs. Do you regap them smaller to BMW MINI specifications or install them as is out of the box?

 

My eye had deceived me! In checking the gap right out of the spark plug box the DENSO plugs for a 2012 Justa came in right to specifications; 0.038"-0.039" just a few thousandths under 1.0mm. They are good to go right from the box.